1. Field of the Invention
The present invention relates to a picture signal processing system, a decoder, a picture signal processing method, and a decoding method suitable for an application that requires high picture quality. In addition, the present invention relates to a picture signal decoding method, a decoding apparatus, a picture signal encoding method, an encoding apparatus, a picture signal processing method, and a processing system for decoding a picture signal that has been compression-encoded by for example MPEG encoding method and encoding the decoded signal.
2. Description of the Related Art
In recent years, the MPEG (Moving Picture Experts Group) encoding method, which is an inter-picture compression encoding method, has been widely used. With the compression-encoding method such as the MPEG encoding method, a record medium can be effectively used. In an editing process for a picture signal that has been encoded by the MPEG encoding method, when a picture signal that has been encoded is decoded and then the decoded picture is re-encoded, the picture quality sometimes deteriorates more than that of a normal encoding process for a video signal. As a cause of such deterioration, encoding parameters such as a picture type and a moving vector of a picture signal encoded by the MPEG encoding method do not match those of a picture signal re-encoded by the MPEG encoding method.
Next, with reference to FIGS. 9A, 9B, and 9C, the case where a picture type of a picture signal that is encoded does not match that of a picture signal that is re-encoded will be described. FIG. 9A shows an example of picture types of input decoded pictures of one GOP (Group Of Pictures) (n=15) where the input decoded pictures are re-encoded. When the phases of picture types are locked as shown in FIG. 9B, as a reference picture for a re-encoding process, an I picture of the input decoded picture shown in FIG. 9A is used as is.
On the other hand, when the phases of picture types are not locked as in the case shown in FIG. 9C, as with the third picture, a B picture whose picture quality largely deteriorates is used as a reference picture. As a result, the accuracy of the re-encoding process deteriorates. Thus, the picture quality largely deteriorates.
Likewise, when another encoding parameter such as a moving vector of a picture signal that is encoded does not match that of a picture signal that is re-encoded, the predictive accuracy deteriorates. Thus, the accuracy of the re-encoding process deteriorates.
On the other hand, when all encoding parameters including a picture type and a moving vector of a picture signal that is encoded are matched with those of a picture signal that is re-encoded, the picture quality hardly deteriorates. However, as the number of encoding parameters increases, the amount of information to be processed increases. Consequently, it is not practical to perform a process for matching all encoding parameters of a picture signal that is encoded with those of a picture signal that is re-encoded. It is known that when a picture type and a moving vector of a picture signal that is encoded are matched with those of a picture signal that is re-encoded, the deterioration of the picture quality can be remarkably suppressed.
However, when high picture quality is required, even if a picture type and a moving vector of a picture signal that is encoded are matched with those of a picture signal that is re-encoded, the deterioration of the picture quality cannot be sufficiently suppressed.
A moving vector represents information of motion of each macro block. Thus, the amount of information of a moving vector is relatively large. Consequently, from a view point of the improvement of the re-encoding process, an encoding parameter that has a smaller amount of information than that of a moving vector and that effectively suppresses the deterioration of the picture quality is required in the case that the structure for matching a moving vector of a picture signal that is encoded is matched with that of a picture signal that is re-encoded cannot be used.
In a system using the MPEG encoding method, an MPEG encoded stream is decoded. The resultant picture signal is converted into a format of a transmission picture signal such as an NTS format. The resultant picture signal is transmitted through a digital VCR or the like and re-encoded by the MPEG encoding method. In another editing system, a picture signal that has been reproduced from a record medium and decoded is combined with an external picture signal. The resultant picture signal is encoded by the MPEG encoding method. The resultant stream is recorded on a record medium. In a dubbing process for recording a video signal recorded on a first record medium to a second record medium by a recorder, a signal of the first record medium is decoded and then re-encoded.
In such examples, when a decoded picture signal is re-encoded, it is preferred to match a picture encoding type of a stream that is re-encoded (an output signal of an encoder) with that of a stream that is encoded (an input signal of a decoder) so as to improve the picture quality of a stream that has been re-encoded and then decoded. In the MPEG encoding method, there are three picture types I, P, and B.
In an I picture (Intra-coded picture), when a picture signal is encoded, information of only one picture is used. Thus, when an encoded picture signal is decoded, information of only the I picture is used. In a P picture (Predictive-coded picture), as a predictive picture (a reference picture for obtaining a difference with the current P picture), an I picture or another P picture that has been decoded is temporally followed by the current P picture. The difference between the current P picture and a motion-compensated predictive picture is encoded for each macro block. Alternatively, the current P picture is encoded for each macro block without obtaining the difference of such pictures. One of those methods is selected whichever higher efficiency is obtained. In a B picture (Bidirectionally predictive-coded picture), as predictive pictures (reference pictures for obtaining a difference with the current B picture), three types of reference pictures are used. The first type reference picture is an I picture or a P picture that has been decoded and that is temporally followed by the current B picture. The second type reference picture is an I picture or a P picture that has been decoded and that is temporally preceded by the current B picture. The third type reference picture is an interpolated picture of the first type reference picture and the second type reference picture. The difference between the current B picture and each of the three type reference pictures that have been motion-compensated is encoded for each macro block. Alternatively, the current B picture is encoded for each macro block without obtaining such a difference. One of those methods is selected whichever higher efficiency is obtained.
Thus, there are a frame intra-coded macro block, a forward inter-frame predictive macro frame (a future macro block is predicted with a past macro block), a backward inter-frame predictive macro block (a past macro block is predicted with a future macro block), and an interpolative macro block (a current macro block is predicted with both a future macro block and a past macro block). All macro blocks in an I picture are intra-frame coded macro blocks. A P picture contains intra-frame coded macro blocks and forward inter-frame predictive macro blocks. A B picture contains the above-described four types of macro blocks.
Generally, the picture quality of a decoded picture of an I picture or a P picture is worse than the picture quality of a decoded picture of a B picture. When a picture is re-encoded, if a decoded picture of a B picture is substituted with an I picture or a P picture and then a B picture is generated, the picture quality of the resultant B picture deteriorates. Thus, when the picture encoding type of a picture that is re-encoded is matched with that of a picture that is encoded, the deterioration of the picture quality in the decoding process and the re-encoding process can be suppressed. To suppress the deterioration of the picture quality, information of a moving vector, a quantizing scale, and so forth (referred to as codic information) that is used in the decoding process is stored. It is preferred to use the codic information in the re-encoding process.
Generally, a decoded picture is converted into a format of a transmission picture signal such as NTSC format and then supplied to an encoder that performs a re-encoding process. Thus, the encoder extracts a decoded picture (an original MPEG encoded area) from the transmission picture signal and re-encodes a decoded picture of which one frame is composed of two fields. The transmission picture signal contains non-decoded-picture information such as a blanking interval and header information. The spatial and temporal positions of decoded pictures in the transmission picture signal are not fixed. In this case, the decoded pictures represent pictures decoded from the original bit stream.
The spatial positions of decoded pictures depend on for example an application format. Depending on whether a transmission picture signal is received from a DVD, an IRD (Integrated Receiver/Decoder), a digital VCR, and so forth, the start line position in the vertical direction and the start position in the horizontal direction of the transmission picture signal vary. In addition, depending on a format, only 352 pixelsxc3x97240 lines may be used as an effective area in 720 pixelsxc3x97480 lines. In the MPEG encoding method, the relation between odd/even cycles in which fields of a transmission picture signal are transmitted and top/bottom fields of a decoded picture in the temporal direction has not been defined.
Thus, when a picture is extracted and re-encoded, an incorrect area may be extracted from the original decoded picture. When one frame is formed with two fields, a combination different from the original combination may be used. Consequently, even if the same picture encoding types are matched, the deterioration of the picture quality cannot be sufficiently suppressed. In addition, when a picture signal is re-encoded, the boundary of a macro block varies from that of the original bit stream. Thus, even if the codic information is re-used, the deterioration of the picture quality cannot be sufficiently suppressed.
Therefore, an object of the present invention is to provide a picture signal processing system, a decoder, a picture signal processing method, and a decoding method that sufficiently suppress the deterioration of picture quality and that allow the amount of transmission information to be small.
A first aspect of the present invention is a picture signal processing system, comprising a decoder for generating the number of encoded bits and/or an average quantizing scale as representative value(s) of encoding parameters of an input encoded picture signal, decoding the input encoded picture signal, generating the decoded picture signal, and outputting the encoding parameters along with the generated decoded picture signal, and an encoder for encoding the decoded picture signal with the encoding parameters.
A second aspect of the present invention is a picture signal processing system, comprising a decoder for decoding an input encoded picture signal, generating a decoded picture signal, superimposing encoding parameters of the encoded picture signal to a signal portion corresponding to an invalid interval of a signal format of the decoded picture signal, and outputting the encoding parameters along with the decoded picture signal, and an encoder for encoding the decoded picture signal with the encoding parameters.
A third aspect of the present invention is a decoder, comprising an encoding parameter generating means for generating the number of encoded bits and/or an average quantizing scale as representative value(s) of encoding parameters of an input encoded picture signal, and a decoding means for decoding the input encoded picture signal and generating the decoded picture signal, wherein the encoding parameters generated by the encoding parameter generating means are output along with the generated decoded picture signal generated by the decoding means.
A fourth aspect of the present invention is a decoder, comprising a decoding means for decoding an input encoded picture signal and generating a decoded picture signal, an outputting means for superimposing encoding parameters of the input encoded picture signal to a signal portion corresponding to an invalid interval of a signal format for transmitting the decoded picture signal generated by the decoding means and outputting the encoding parameters along with the decoded picture signal.
A fifth aspect of the present invention is a picture signal processing method, comprising the steps of generating the number of encoded bits and/or an average quantizing scale as representative value(s) of encoding parameters of an input encoded picture signal, decoding the input encoded picture signal and generating the decoded picture signal, outputting the encoding parameters along with the generated decoded picture signal, and encoding the decoded picture signal with the encoding parameters.
A sixth aspect of the present invention is a picture signal processing method, comprising the steps of decoding an input encoded picture signal and generating a decoded picture signal, superimposing encoding parameters of the input encoded picture signal to a signal portion corresponding to an invalid interval of a signal format for transmitting the generated decoded picture signal and outputting the encoding parameters along with the decoded picture signal, and encoding the decoded picture signal with the encoding parameters.
A seventh aspect of the present invention is a decoding method, comprising the steps of generating the number of encoding bits and/or an average quantizing scale as representative values of encoding parameters of an input encoded picture signal, decoding the input encoded picture signal and generating a decoded picture signal, and outputting the encoding parameters along with the decoded picture signal.
An eighth aspect of the present invention is a decoding method, comprising the steps of decoding an input encoded picture signal and generating a decoded picture signal, and superimposing encoding parameters of the input encoded picture signal to a signal portion corresponding to an invalid interval of a signal format for transmitting the generated decoded picture signal and outputting the encoding parameters along with the decoded picture signal.
A ninth aspect of the present invention is a picture signal decoding method for decoding data that has been encoded by an inter-picture predictive encoding process, comprising the steps of decoding the data that has been encoded by the inter-picture predictive decoding process, converting the decoded picture signal into a transmission picture signal, and outputting control information along with the transmission picture signal, wherein the control information is composed of an indicator of a display start field of the decoded picture and a display start line of the decoded picture, and wherein the control information is superimposed with the transmission picture signal or output to a signal line different from a signal line for the transmission picture signal.
A tenth aspect of the present invention is a picture signal encoding method for encoding a decoded picture of data that has been encoded by an inter-picture predictive encoding method, comprising the steps of receiving control information composed of a transmission picture signal, an indicator, and data, the transmission picture signal being composed of a decoded picture, the indicator representing a display start field of the decoded picture, the data representing a display start line of the decoded picture, forming an encoding target area of the transmission picture signal with the control information, and performing the inter-picture predictive encoding process for the encoding target area.
An eleventh aspect of the present invention is a picture signal processing method for decoding data that has been encoded by an inter-picture predictive encoding process and encoding the decoded data, comprising the steps of decoding the data that has been encoded by the inter-picture predictive encoding process, converting the decoded picture signal into a transmission picture signal, outputting control signal along with a transmission picture signal, the control signal being composed of an indicator and data, the indicator representing a display start field of the decoded picture, the data representing a display start line of the decoded picture, receiving the transmission picture signal and the control information, forming an encoding target area of the transmission picture signal with the control information, and performing the inter-picture predictive encoding process for the encoding target area.
A twelfth aspect of the present invention is a decoding apparatus for decoding data that has been encoded by an inter-picture predictive encoding method, comprising a decoder for decoding the data that has been encoded by the inter-picture predictive encoding process, and a means for converting the decoded picture signal into a transmission picture signal and outputting control signal along with a transmission picture signal, wherein the control signal is composed of an indicator and data, the indicator representing a display start field of the decoded picture, the data representing a display start line of the decoded picture.
A thirteenth aspect of the present invention is a picture signal encoding method for encoding a decoded picture of data that has been encoded by an inter-picture predictive encoding process, comprising the steps of receiving control information composed of a transmission picture signal, an indicator, and data, the transmission picture signal being composed of the decoded picture, the indicator representing a display start field of the decoded picture, the data representing a display start line of the decoded picture, forming an encoding target area for the transmission picture signal, and performing the inter-picture predictive encoding process for the encoding target area.
A fourteenth aspect of the present invention is a picture signal processing system for decoding data that has been encoded by an inter-picture predictive encoding process and encoding the decoded data, comprising a decoder for decoding the data that has been encoded by the inter-picture predictive encoding process, a means for converting the decoded picture signal into a transmission picture signal and outputting control information along with the transmission picture signal, the control information being composed of an indicator and data, the indicator representing a display start field of the decoded picture, the data representing a display start line of the decoded picture, a means for forming an encoding target area of the transmission picture signal with the control information, and performing an inter-picture predicting encoding process for the encoding target area.
According to the present invention, an encoding parameter that is used in a first picture encoding process is supplied to an encoder that performs a re-encoding process. Thus, with the same encoding parameter used in the first inter-picture compression-encoding process, the re-encoding process can be performed.
In particular, when the number of encoded bits, an average quantizing scale, and so forth used in the first encoding process are supplied to the encoder that performs the re-encoding process, the number of encoded bits in the first encoding process can be matched with that in the re-encoding process.
In addition, according to the present invention, when a decoded picture is converted into a transmission picture signal and the transmission picture signal is re-encoded, temporal information and spatial information of the decoded picture are supplied as control information to the re-encoder. Thus, the re-encoder can re-encode the decoded picture with the same temporal and spatial relations with the original bit stream. Consequently, the deterioration of the picture quality in the decoding process and the re-encoding process can be effectively suppressed.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.